HDRenderPipeline: Add include shader path for external generated shader

ScriptableRenderPipeline/Core/Editor/CoreEditorUtils.cs

-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq.Expressions;
 using System.Text;
             }
 
             return state;
+        }
+
+        public static void RemoveMaterialKeywords(Material material)
+        {
+            material.shaderKeywords = null;
         }
     }
 }

ScriptableRenderPipeline/HDRenderPipeline/Editor/HDEditorUtils.cs

-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.IO;
 using UnityEngine;
 
             return path;
         }
 
-        // TODO: The two following functions depend on HDRP, they should be made generic
+        // TODO: The following functions depend on HDRP, they should be made generic
+        public static string GetScriptableRenderPipelinePath()
+        {
+            var hdrpPath = GetHDRenderPipelinePath();
+            var fullPath = Path.GetFullPath(hdrpPath + "../");
+            var relativePath = fullPath.Substring(fullPath.IndexOf("Assets"));
+            return relativePath.Replace("\\", "/") + "/";
+        }
+
         public static string GetPostProcessingPath()
         {
             var hdrpPath = GetHDRenderPipelinePath();
             MaterialResetter resetter;
             if (k_MaterialResetters.TryGetValue(material.shader.name, out resetter))
             {
-                RemoveMaterialKeywords(material);
+                CoreEditorUtils.RemoveMaterialKeywords(material);
-        }
-
-        public static void RemoveMaterialKeywords(Material material)
-        {
-            material.shaderKeywords = null;
         }
     }
 }

ScriptableRenderPipeline/HDRenderPipeline/Editor/HDRenderPipelineMenuItems.cs

                 {
                     mat.shader = litShader;
                     // We remove all keyword already present
-                    HDEditorUtils.RemoveMaterialKeywords(mat);
+                    CoreEditorUtils.RemoveMaterialKeywords(mat);
                     LitGUI.SetupMaterialKeywordsAndPass(mat);
                     EditorUtility.SetDirty(mat);
                 }
                     // We remove all keyword already present
-                    HDEditorUtils.RemoveMaterialKeywords(mat);
+                    CoreEditorUtils.RemoveMaterialKeywords(mat);
                     LayeredLitGUI.SetupMaterialKeywordsAndPass(mat);
                     EditorUtility.SetDirty(mat);
                 }

ScriptableRenderPipeline/HDRenderPipeline/Editor/HDDefaultShaderIncludes.cs

+using UnityEditor.Experimental.Rendering.HDPipeline;
+
+namespace UnityEditor
+{
+    internal static class HDDefaultShaderIncludes
+    {
+        static string s_RenderPipelinePath
+        {
+            get { return HDEditorUtils.GetScriptableRenderPipelinePath(); }
+        }
+
+        [ShaderIncludePath]
+        public static string[] GetPaths()
+        {
+            return new[]
+            {
+                s_RenderPipelinePath
+            };
+        }
+    }
+}

ScriptableRenderPipeline/HDRenderPipeline/Editor/HDDefaultShaderIncludes.cs.meta

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